Valve lapping

[johnray13]

I have a 6.5kw 2 cylinder air cooled onan nhd. The manual states not to lap the interference valves (45° seat angle and 44° valve angle)

Is there any harm to lapping them and whats the reason? I noticed older manuals for this same block only suggest avoiding lapping rather than stating flat out not to do it.

John

 

[m-35tom]

there is simply no reason to lap, nothing to be gained. you can use prussian blue to confirm the fit, that is all you need.

 

[phil2968]

Lapping would destroy that 1° angle difference.

 

[M543A2]

Phil 2968 is correct. Lapping could destroy the interference valve angle. Checking contact with Prussian Blue as M-35tom says will tell you how the fit is.